I. Field of the Invention
The present invention is directed to mitigating radiation induced faults. More particularly, the present invention is directed to a method and/or system for handling an inherent susceptibility of Commercial-Off-The-Shelf (“COTS”) components to Single Event Upsets (“SEUs”). The invention is particularly useful in providing real time environmental sensing, utilizing a COTS based computer architecture that supports adaptable configuration levels of fault tolerance, while also increasing performance and efficiency while maintaining reliable operation. However, aspects of the invention may be equally applicable in other scenarios as well.
II. Description of Related Art
Science and defense missions alike have increasing demands for data returns from their space born assets. In more recent times, there has been an increase in the capability of the instruments deployed in space. For example, such an increase has been discussed in the following references which are herein entirely incorporated by reference and to which the reader is directed to for further information: “An Overview of Earth Science Enterprise”, NASA Goddard Space Flight Center, FS-2002-3-040-GSFC, March 2002; Wallace M. Porter And Harry T. Enmark, “A System Overview of The Airborne Visible/Infrared Imaging Spectrometer (AVIRIS)”, JPL Pasadena, Calif.; and H. L. Huang, “Data Compression of High-spectral Resolution Measurements”, Satellite Direct Readout Conference for the Americas, December 2002.
In one typical approach for data gathering, data compression and data transmission no longer appears sustainable. It is difficult to transmit a vast amount of data via available downlink channels in a reasonable period of time. One proposed solution to such a situation is to reduce demand on a downlink by moving processing away from earth and onto the space born asset.
However, there are certain limitations to such an approach. For example, this approach is hampered by limited capabilities of conventional on-board processors. It is also prohibitive based on the cost of developing radiation hardened high-performance electronics. Such issues are discussed in the references J. Marshall and R. Berger, “A Processor Solution for the Second Century of Powered Space Flight,” Digital Avionics Systems Conferences, 2000. Proceedings. DASC. The 19th Volume: 2, 7-13 Oct. 2000, Pages: 8.A.2—1-8.A.2—8 and Gary R. Brown, “Radiation Hardened PowerPC 603e™ Based Single Board Computer,” 20th Digital Avionics Systems, 2001. October 2001 herein entirely incorporated by reference and to which the reader is directed for further information.
Based in part on these perceived concerns, the relevant industry has considered the use of COTS components. For example, such general considerations are generally described in the reference E. R. Prado et al., “A Standard Approach to Spaceborne Payload Data Processing,” IEEE Aerospace Conference, March 2001 herein entirely incorporated by reference and to which the reader is directed for further information. Furthermore, a more recent adoption of silicon-on-insulator (“SOI”) technology by COTS integrated circuit foundries has also resulted in devices with moderate space radiation tolerance. See, e.g., the references F. Irom et al., “Single-Event Upset in Evolving Commercial Silicon-on-Insulator Microprocessor Technologies, Nuclear and Space Radiation Effects Conference 2003 and Xilinx Corporation, “QPro Virtex 2.5V Radiation Hardened FPGA,” Xilinx Web site http://www.xilinx.com/, November 2001 herein entirely incorporated by reference and to which the reader is directed for further information.
Despite such progress, COTS components continue to be somewhat highly susceptible to SEUs. One popular approach for mitigating such SEUs is to employ fixed component level redundancy. See, e.g., Daniel P. Siewiorek and Robert S. Swarz, Reliable Computer Systems Design and Evaluation 3rd edition, MA: AK Peters Ltd., 1998 herein entirely incorporated by reference and to which the reader is directed for further information. However, one disadvantage of utilizing fixed component level redundancy is its low efficiency and its unrealized system capacity.
Certain conventional onboard processing computers consist mostly of radiation hardened components based on COTS equivalents. Though COTS compatibility offers certain perceived benefits, including adoption of commercial software, typically large amounts of Non-Recurring Engineering (NRE) are often required for an initial silicon implementation. Additionally, radiation hardened components often lag their commercial counterparts in overall performance and capability by at least 1 to 2 orders of magnitude. There are a number of factors that contribute to this deficiency. One such factor relates to radiation-hardening techniques and that such techniques for microelectronics require the use of fixed transistor or gate level redundancy. This additional logic increases the power required to perform the same unit of computation.
An approach towards improvement concerns the use of true COTS microprocessors and Field Programmable Gate Arrays (“FPGAs”). Typically, such an approach avoids the high cost and long development time associated with radiation hardened equivalents. However, true COTS devices are typically quite susceptible to SEUs. One popular SEU mitigation approach is to use component level N-module redundancy. However, such N-module redundancy often results in low efficiency and low capacity due to an overhead that often approaches ⅔, or more.
Furthermore, the level of redundancy is fixed and is often unnecessary. To overcome the deficiencies of fixed redundancy, two characteristics of space missions may be focused on: first, the variability of space environment and second, the task level criticality. Most missions will have a mix of processes with varying criticality. This characteristic of mission processing can be exploited to increase a systems efficiency by applying redundancy at a task level. Furthermore, there is a variability involved in a space environment and this variability provides a temporal and orbital position dependency on the necessary redundancy.
There is, therefore, a general need for a method and/or system for the mitigation of radiation induced faults (“SEUs”). There is also a general need for a method and system that can utilize lower cost COTS components in space which exhibit acceptable overall TID and Latch Up characteristics, but are still susceptible to SEUs. A further need exists for a system and/or method that facilitates the use of COTS components in SEU abundant environments, while also maintaining adequate levels of system efficiency and capacity.
There is a further need for such systems and methods of accomplishing such adequate levels of system efficiency and capacity by adaptively configuring a level of fault tolerance in a system as mandated by a mission environment and/or a mission application. Consequently, there is a general need for real time environmental sensing, utilizing a COTS based computer architecture that supports adaptable configuration levels of fault tolerance, while also optimizing performance and efficiency while maintaining reliable operation.